This invention relates to a flexible bearing assembly for securing a rotating shaft maintained within a bearing. More particularly the present invention concerns a combination spring and damper formed by cutting slots in a solid resilient member to form damper arms which both assist in providing a spring force for centering the shaft and providing improved amplified squeeze film-type damping.
In a turbomachine it is desirable to support a shaft for high speed rotation. It is necessary to provide a bearing about the shaft to minimize rolling resistance of the shaft while securing the shaft in the appropriate position. The support structure for securing the shaft should be a stiff as possible. The bearing retainer supporting the bearing must be sufficiently resilient that abnormal displacement in any specific direction is resisted and must include means to act as a damper. A typical bearing assembly provides means for centering the assembly to maintain the shaft in the desired position. A spring means for tuning damping of the shaft to the desired frequency also may act to limit displacement during unsual operating conditions.
Additionally if the shaft is to be operated above the first critical speed or any higher critical speed it is necessary to provide damping. Without damping the vibratory force at critical speed will theoretically become infinite. Hence it is necessary to provide damping to maintain the structural integrity of the turbomachine support as it passes through critical speeds.
Previous flexible damped bearing supports such as may be seen in U.S. Pat. Nos. 4,027,931 and 3,979,155 disclose a bearing for securing the rotor and damping means mounted together with the bearing providing the necessary damping. Located to the side of the damper is a cage-type spring extending about the shaft. The cage spring and the damper are mounted axially relative to the shaft and take up considerable shaft space. Additionally they are separate members which must be joined in a structural arrangement as shown in these patents. Similar cage-type structural supports have been utilized in turbine engines such as aircraft engines.
One effort at providing an integral damper and spring for maintaining the shaft in position is shown in U.S. Pat. No. 3,394,971. Therein a spring is spaced circumferentially about the bearing race and a support structure and is attached to each such that some flexure is provided between the two. The spring is a separate structure mounted to the exterior of the bearing race and the support by rivets or similar means at spaced locations. This particular bearing provided no integral damping therewith.
The present invention provides a single structure capable of providing both damping and a spring to tune the damping within a single annular element. Additionally no cage spring nor other axially extending device is necessary and the length of the shaft being utilized may be accordingly reduced. The device is capable of being tuned to obtain the desired damping and spring force characteristics by the design of the damper arms and pivot points within the damper body of the device.